Firebox door shutter of a barbecue oven



FIG. 1 is a left perspective view of a firebox door shutter of a barbecue oven;

FIG. 2 is an enlarged front view thereof;

FIG. 3 is a right perspective view of a firebox door shutter of a barbecue oven with a different type of barbecue oven shown in broken lines; and,

FIG. 4 is an enlarged front view thereof.

The broken lines showing portions of the barbecue oven form no part of the claimed design. 

CLAIM The ornamental design for a firebox door shutter of a barbecue oven, as shown and described. 